Certain electronic devices may track position for various terrestrial and space applications. Such devices include Global Positioning Systems (“GPS”) and IMUs. IMU measurements are qualitatively different from radiometric measurements used by systems such as GPS. GPS uses time of flight, whereas IMUs measure acceleration and changes in angle (i.e., inertial measurements) via mechanisms such as accelerometers measuring load cells, spring displacements, etc. The inertial measurements are intrinsic to the physics of the body they are on, whereas radiometric measurements are used to calculate position mathematically as legs of a triangle.
IMUs may be particularly beneficial in navigation systems where it is not possible to use an external navigation source, such as GPS, for a period of time. For example, for spacesuit navigation on the lunar surface, GPS is generally not usable because the moon currently lacks a network of satellites required to effectively facilitate GPS. Four satellites are required to determine horizontal position and height (i.e., location in three dimensions), as well as receiver clock offset.
However, to be most effective and simple to integrate into an overall navigation system consisting of many sensors, IMU data generally should be closely synchronized in time to other sensors in the system, such as GPS or other radiometric measurements when available. This generally requires a precise time-stamp technique as well as external synchronization pulse triggering. Conventional systems are stand-alone IMU applications that often rely on GPS as a time stamping device rather than on a triggering mechanism to synchronize collection of IMU data. The high drift rates of Micro-Electromechanical System (“MEMS”) IMUs, or the inclusion of gravity sensors to correct the drift, make these stand-alone solutions particularly impractical for various applications, such as studying lunar surface navigation. Accordingly, an IMU system that can effectively synchronize with other system sensors without relying solely on time stamping may be beneficial.